Chapter 28.4, Problem 1CS

Core Skill: Modeling The goal of this modeling challenge is to make a simplified model of the one shown in Figure 28.29, to determine if the latter represents a life cycle that is diploid dominant, haploid dominant, or an alternation of generations.

Modeling Challenge: Chapter 16 describes the three basic types of eukaryotic sexual life cycles (refer back to Figure 16.14). These cycles are modeled by circular diagrams that show life phases connected by the processes of fertilization, meiosis, and mitotic cell divisions. Animals display a diploid-dominant life cycle; fungi have a haploid-dominant life cycle, and the life cycle of plants involves an alternation of a haploid gametophyte with a diploid sporophyte. This chapter reveals that all of these basic life cycle types occur among protists. Use the detailed sexual life cycle shown in Figure 28.29 to identify the life cycle type (diploid dominant, haploid dominant, or alternation of generations) that is characteristic of Plasmodium. To make this decision, draw a very simple circular model representing the cycling of Plasmodium between haploid and diploid life phases and the occurrence of fertilization, meiosis and mitotic cell divisions. Then compare your simple model to the three models shown in Figure 16.14.

Figure 28.29 Diagram of the life cycle of Plasmodium falciparum, a species that causes malaria in humans. This life cycle requires two alternate hosts, humans and Anopheles mosquitoes. Parasite life stages known as sporozoites are transmitted by a mosquito bite, then infect the liver. The parasite life stages known as merozoites are produced in the liver, and infect red blood cells.

Figure 16.14 A comparison of three types of life cycles for sexually reproducing organisms.